Solvent Extraction - Ultraviolet Spectroscopy

Straightforward UV spectroscopy is liable to be in error because of interference by other highly absorbing impurities that may be present in the sample [59-62], Interference by such impurities in direct UV spectroscopy has been overcome or minimised by selective solvent extraction or by chromatography [60], However, within prescribed limits UV spectroscopy is of use and, as an example, procedures are described next for the determination of lonol (2,6-di- e -butyl-p-cresol) and of Santonox R (4,4 -thio-bis-6-terUbutyl-m-cresol) in polyolefins [63-66], 

Certain additives, e,g, calcium stearate and thiodipropionate, do not interfere in the determination. Other phenolic antioxidants, e,g, lonox 330, Topanol CA and Santonox R, do interfere. 

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Similarly, organic liquids have a variety of applications. For example, hexane, which frequently contains impurities such as aromatic compounds, is used in a variety of applications for extracting non-polar chemicals from samples. The presence of impurities in the hexane may or may not be important for such applications. If, however, the hexane is to be used as a solvent for ultraviolet spectroscopy or for HPLC analysis with UV absorbance or fluorescence detection, the presence of aromatic impurities will render the hexane less transparent in the UV region. It is important to select the appropriate grade for the task you have. As an example, three different specifications for n-hexane ( Distol F , Certified HPLC and Certified AR ), available from Fisher Scientific UK, are shown in Figure 5.5 [10]. You will see that the suppliers provide extra, valuable information in their catalogue. 

Solvents and substances that are specified as pure for a particular purpose may, in fact, be quite impure for other uses. Absolute ethanol may contain traces of benzene, which makes it unsuitable for ultraviolet spectroscopy, or plasticizers which make it unsuitable for use in solvent extraction. 

Several spectroscopic techniques, namely, Ultraviolet-Visible Spectroscopy (UV-Vis), Infrared (IR), Nuclear Magnetic Resonance (NMR), etc., have been used for understanding the mechanism of solvent-extraction processes and identification of extracted species. Berthon et al. reviewed the use of NMR techniques in solvent-extraction studies for monoamides, malonamides, picolinamides, and TBP (116, 117). NMR spectroscopy was used as a tool to identify the structural parameters that control selectivity and efficiency of extraction of metal ions. 13C NMR relaxation-time data were used to determine the distances between the carbon atoms of the monoamide ligands and the actinides centers. The II, 2H, and 13C NMR spectra analysis of the solvent organic phases indicated malonamide dimer formation at low concentrations. However, at higher ligand concentrations, micelle formation was observed. NMR studies were also used to understand nitric acid extraction mechanisms. Before obtaining conformational information from 13C relaxation times, the stoichiometries of the... 

The following abbreviations are used UV = ultraviolet oxidation CO = chemical oxidation SE = solvent extraction XAD = adsorption on Amberlite XAD-2 resin AAS = atomic absorption spectrophotometry S = visible spectrophotometry XRF = X-ray fluorescence spectroscopy NAA = neutron activation analysis. 

For the purification of compounds, methods including molecular filtration, solid phase extraction (SPE, SPME), solvent extraction, and a variety of basic chromatographic techniques (thin layer, low pressure, ion exchange, size exclusion, etc.), HPLC, and GC (with derivatization of nonvolatile compounds) can be used. Additionally, instrumentation to identify compounds is available, such as the different spectrometric applications, including infrared (IR), mass (MS), ultraviolet and visible (UV-Vis), and NMR spectroscopy. In recent years, the so-called hyphenated techniques (combined chromatographic and spectral methods such as... 

Elution with chloroform removes BHT only as the first fraction. Continued elution of the column with solutions of 10% water in methanol removes Santowhite powder or Santonox R as a separate pure fraction, free from BHT. Additives can then be determined in the respective extracts after they have been diluted to a standard volume with solvent by ultraviolet (UV) spectroscopy. 

Generally, methods are based on solvent extraction of the additive followed by analysis for the extracted additive by a suitable physical technique such as visible spectrophotometry of the coupled antioxidant, redox spectrophotometric methods, ultraviolet spectroscopy, infrared spectroscopy, gas chromatography, thin-layer chromatography or column chromatography. In general, direct chemical methods of analysis have not foimd favour. These include potentiometric titration with standard sodium isopropoxide in pyridine medium or reaction of the antioxidant with excess standard potassium bromide-potassium bromate (ie. free bromine) and estimation of the unused bromine by addition of potassium iodide and determination of the iodine produced by titration with sodium thiosulphate to the starch end-point. ... 

Drug Administration extraction procedures can be concentrated by evaporation in a water bath. No satisfactory extraction procedure has been found for concentrating the liquid paraffin extractant. Finally, the extracts are dried with anhydrous sodium sulfate, evaporated to dryness and made up to 2 ml with distilled water or another appropriate spectroscopic solvent, preparatory to ultraviolet spectroscopy. Such... 

The action of all UV absorbers depends on the Lambert-Beer law, and the absorption properties of the UV absorber. The further the absorption edge extends into the near UV region, the more UV light can be filtered out. Of the four UV absorber classes shown above, the hydroxyphenylbenzotriazoles have the broadest absorption band [5.8], [5.12], In addition to thermal stability [5.12] and stability to extraction with water or organic solvents, photochemical stability is important [5.13]-[5.15], Ultraviolet reflection spectroscopy can be used to establish whether the employed UV absorber is still effective, even after several years external weathering [5.16]. 

A suitable extract of the polymer is applied to a thin layer plate and the plate migrated with suitable development solvents to separate the individual polymer additives present. Examination of the plate under an ultraviolet light or the application of spray reagents reveals the separated additives. A second plate is now prepared and the bands of plate which contain the separated additives are removed and each band is separately extracted with a suitable solvent to extract the additives. These extracts are then concentrated and dissolved in suitable spectroscopic solvents for infrared and/or ultra-violet spectroscopy to identify and/or determine each additive. 

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